There has long existed a need for a light-weight, collapsible ladder that may be secured to, for example, a window or other aperture of a multi-story building in order to provide occupants of the building a secondary route of escape during a fire. Many patents disclose inventions which are intended to fulfill this long-felt need. For example, U.S. Pat. No. 190,342 to Lake discloses a collapsible ladder having rungs that are secured together by metal rods which are formed into rectangular shapes so as to secure two rungs together in a non-collapsed condition of the ladder.
Each rung (except the bottom rung) has two sets of holes which are spaced forward and backward on the tread of the rung, with one set of holes for securing the ladder rung from above and the other set of holes for securing the next ladder rung below.
U.S. Pat. No. 314,287 to Feigenbaum discloses a rope ladder having round rungs which fit between the floor joists of a building, the ladder being deployed when a trap door is removed and put out of the way so as to allow the ladder to be let down to the floor below.
U.S. Pat. No. 1,424,115 to Nileon discloses a rope ladder having hollow tubular rungs, with the ends of the rungs having one-half removed so as to be semi-circular in cross-section and bent at a right angle to tightly bind a cable, and at the same time engage a wall of a building, whereby the ladder rung will be held away from the side of a building a distance sufficient to permit the user to gain a foot hold on the ladder rung.
U.S. Pat. No. 4,098,372 to Luckey discloses a collapsible ladder made of a non-combustible material having two flexible strings with rungs threaded thereon at spaced distances.
These rungs have divergent limbs so that, when the ladder is collapsed, the rungs may be stacked on one another in such a way as to leave between each pair of adjacent rungs a free hollow area for complete reception of segments of a cable or strip elements which support the rungs when the ladder is in use.
U.S. Pat. No. 4,298,097 to Eriksson discloses an escape ladder assembled of rungs, the ends of which are attached between flexible lateral members, with the rungs being of metal material and capable of being stacked, and with the upper portion of the escape-ladder intended to be attached to a wall or the like.
U.S. Pat. No. 4,846,306 to Ventz discloses a rope escape ladder including a pair of parallel support ropes and a series of narrow rungs disposed between the support ropes, wherein the rungs are so narrow that no more than one hand or one foot can be placed on a rung at a time.
U.S. Pat. No. 5,605,205 to Douglas et al discloses a collapsible ladder having hooks for securing to a window surface, a rigid spacing member extending between the hooks and defining a slot, an elongated flexible support element of nylon rope or steel cable attached to the hooks, a plurality of rungs, formed from a molding process, that stack and nest with a storage region between each rung for storing the flexible support, a fastener to connect each rung to the flexible support, and a cover for holding the rungs in the nested state. The cover has a neck portion, and a handle which extends through the slot in the rigid spacing member. The handle is movable in the slot to thereby release the cover and deploy the ladder to the extended state.
Despite a myriad of patents having addressed the need for a light-weight, collapsible ladder for over a century of development, there remains the need for a light-weight escape ladder which can be easily deployed and safely descended in a fire emergency in case the primary means of escape (such as a stairwell) is blocked and wherein, in the collapsed state, the rungs of the ladder nest to a high degree of compactness.